In my windows 7 i have 2 accounts: an administrator account (let's call it "admin") and a standard user (called "reader"). In the SP2010 central administration i have correctly added both accounts as "managed accounts". In my site i have modified the "site permissions": "admin" account was already in the "[Site collection name] Owners" group, and i have added the "reader" account to the "[Site collection name] Visitors" group.

When i open a SP website i have to login: let's say i log in as "reader". Then i want to log in as "admin", so i select "Sign in as a different user" in the top-right corner of the page. Now when i insert username and password of the "admin" account, i get some kind of error, as if the password is wrong (but i get no message, just the same window again asking me for username and password). At the third attempt, i get the 401 UNAUTHORIZED page. But when i close the page a re-open it, i result logged in as "admin", without having to insert username and password!